1. Technical Field
The present invention relates to a nearly deterministic single-photon source that preferably is useful for quantum cryptography (quantum key distribution) and for building optical quantum computers at a scale large enough to represent a major advance over classical computing.
2. Description of the Related Art
Current single-photon sources have serious limitations for use in quantum computing or communications. Ideally, a single-photon source would reliably and repeatedly emit exactly one photon, either at an arbitrarily requested time (on-demand) or at well-defined time intervals (periodic). In practice, currently available sources are effectively non-deterministic. Some emit photons at random times, making it difficult to coordinate the multiple sources required in systems such as quantum logic processors. Sources that can be driven periodically typically produce a random distribution in the number of photons (e.g., zero, one, or more than one) that are emitted in successive pulses.
The probability of single-photon emission in a given clock cycle is often very low, particularly when conventional approaches are used to minimize the probability of multi-photon emission. Multi-photon emission can cause errors in quantum logic gates, or leak information that reduces the security or decreases the throughput on quantum communications links.